1. Field of the Invention
This invention relates to a sintered ferrite body useful as various magnetic materials, a chip inductor using the sintered body as a magnetic material, and a composite LC part having capacitor and inductor sections in a common chip.
2. Prior Art
A variety of ferrites have been used as various magnetic cores because of their magnetic properties. Among others, nickel base ferrites including Ni ferrites, Ni-Zn ferrites, and Ni-Cu-Zn ferrites have been widely used as low-temperature sinterable material to which printing and green sheet techniques are applicable.
Sintered ferrite bodies, however, have unsatisfactory mechanical strength. The sintering temperature must be raised to increase the density of a sintered body before the mechanical strength can be enhanced. This undesirably invites an increase of manufacturing expense.
Japanese Patent Application Kokai Nos. 58-135133, 58-135606, 58-135607, 58-135608 and 58-135609 disclose to add glass to ferrite to reduce shrinkage upon sintering, but the specific composition of glass is not disclosed therein. These sintered bodies are insufficient in denisty, mechanical strength, and high-frequency properties. These drawbacks are assumed to be caused by non-use of the borosilicate glass which is used in the present invention as described later.
Japanese Patent Application Kokai No. 51-151331 and U.S. Pat. No. 4,540,500 disclose ferrite having up to 5% by weight of lithium borosilicate glass added thereto. The excellent effects of the present invention will not be attained in the ferrite body because of a less amount of glass.
Japanese Patent Application Kokai No. 59-90915 discloses to form a glass intermediate layer between a conductive layer and an insulating layer. Such a construction will cause Q value drop and insufficient control of coefficient of linear expansion in forming a chip inductor.
Chip inductors and composite LC parts having inductor and capacitor sections in a common chip are known as typical parts in which ferrite finds application. Chip inductors are usually prepared by forming a paste of ferrite and applying the ferrite paste by printing or green sheet technique to form a laminate having an internal conductor embedded therein, followed by sintering. They also suffer from the problems that mechanical strength is low and the sintering temperature must be raised to increase mechanical strength.
These inductors have unsatisfactory frequency response of inductance and Q value. For example, their inductance and Q value approach substantially zero at a high frequency region in excess of 200 kHz. Frequency response may be improved by using a non-magnetic ceramic in an inductor section to form a coreless coil. The resulting inductor, however, has an insufficient inductance and Q value.
Composite LC parts having inductor and capacitor sections in a common chip suffer from problems that separation or warpage occurs at the LC interface during sintering because of the difference of shrinkage between the ferrite of the inductor section and the dielectric material of the capacitor section and a crack occurs because of the difference of coefficient of linear expansion, failing to fulfil the function as a surface packaged part.
Sintered ferrite bodies find other applications as various magnetic cores, magnetic shields, electromagnetic radiation shields, and attenuators. In these applications, it is also desired to improve sintering temperature, sintered density, and mechanical strength as well as frequency response of electromagnetic properties such as magnetic permeability loss.